The purpose of this study is to determine the influence of sex hormones on cognition in the aged. We will study changes in cognition in subjects supplemented with either estrogen (women) or testosterone (men) or placebo. Subjects will be tested on a variety of cognitive tasks that 1) show declines in the healthy aged, 2) show sex differences in younger subjects, 3) assesses the integrity of specific cognitive and neural systems (visual attention, visual perception, and visual memory).